The present invention relates to facsimile coding systems and methods for use in the fields of facsimile compression, optical character recognition, and image correlation. In the prior art, most facsimile coding systems have generally been based upon the concept of run-length coding, which provides relatively high compression ratios for a graphic type document or an alphanumeric document containing a small amount of text. However, the achievable compression ratio drops appreciably if a document is densely filled with alphanumeric symbols because the black and white run-lengths become quite short. Dense alphanumeric documents can be efficiently coded by character recognition techniques in which individual characters are detected and coded by a prototype library code. However, such a method cannot effectively handle documents containing a mixture of alphanumerics and graphics.
One prior art approach to this problem has been to segment a document into strips containing alphanumeric text or graphics data, and then code the former by character matching and the latter by run-length coding. The problems with this approach are the difficulty of document segmentation and the drop in compression performance if the segmentation is not accurate.
In view of the above background, it is an objective of the present invention to provide an improved facsimile coding system.